CN115236152B - Method for simultaneously detecting lead and arsenic, detection electrode, electrochemical sensor and preparation method - Google Patents
Method for simultaneously detecting lead and arsenic, detection electrode, electrochemical sensor and preparation method Download PDFInfo
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- 239000004927 clay Substances 0.000 claims description 12
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 10
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- 239000003792 electrolyte Substances 0.000 claims description 7
- 239000002253 acid Substances 0.000 claims description 6
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- 238000004070 electrodeposition Methods 0.000 claims description 6
- 238000010828 elution Methods 0.000 claims description 6
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 5
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- -1 arsenic ions Chemical class 0.000 claims description 4
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- 238000004832 voltammetry Methods 0.000 claims description 3
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 abstract description 46
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- 229910001385 heavy metal Inorganic materials 0.000 description 12
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- 238000000835 electrochemical detection Methods 0.000 description 9
- 238000001075 voltammogram Methods 0.000 description 8
- 235000014653 Carica parviflora Nutrition 0.000 description 7
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- 238000005171 square wave anodic stripping voltammetry Methods 0.000 description 5
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- 229940075397 calomel Drugs 0.000 description 2
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- ZOMNIUBKTOKEHS-UHFFFAOYSA-L dimercury dichloride Chemical compound Cl[Hg][Hg]Cl ZOMNIUBKTOKEHS-UHFFFAOYSA-L 0.000 description 2
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- MKYBYDHXWVHEJW-UHFFFAOYSA-N N-[1-oxo-1-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propan-2-yl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(C(C)NC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 MKYBYDHXWVHEJW-UHFFFAOYSA-N 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/308—Electrodes, e.g. test electrodes; Half-cells at least partially made of carbon
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/48—Systems using polarography, i.e. measuring changes in current under a slowly-varying voltage
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- Chemical Kinetics & Catalysis (AREA)
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- Molecular Biology (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
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- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
Abstract
The invention provides a method for simultaneously detecting lead and arsenic, a detection electrode, an electrochemical sensor and preparation. The detection electrode comprises a graphite core and a nano-gold coating. The graphite core surface has a graphite skin layer comprising a plurality of graphite layers. The nano-gold coating is covered on the graphite surface layer and comprises a plurality of three-dimensional nano-gold particles. The graphite surface layer has larger specific surface area, can provide larger accommodation space for the nano gold coating, and can accommodate more nano gold particles. The gold nanoparticle has a three-dimensional structure and a large specific surface area. Therefore, the whole specific surface area of the nano gold coating is larger, and the electrochemical activity of the detection electrode is high. In addition, the contact area between the gold nanoparticle with the three-dimensional structure and the graphite surface layer is increased, so that the gold nanoparticle coating layer is firmly combined with the graphite core, the stability of the detection electrode is better, the service life is long, and the data repeatability is good.
Description
Technical Field
The invention relates to the technical field of electrochemical sensing, in particular to a method for simultaneously detecting lead and arsenic, a detection electrode, an electrochemical sensor and preparation.
Background
Heavy metal pollution is increasingly threatening to humans and the environment, and once heavy metal ions are immersed in the polluted environment, they are not decomposed for decades or more. Heavy metal ions enter the human body system through food, water sources, air and the like, and are continuously accumulated in the body, so that serious injury is caused to the human body. Arsenic interferes with the normal metabolism of cells, which can lead to lesions, while lead can lead to nerve and kidney damage, with higher levels even leading to death. With the continuous development of the industrial market, lead and arsenic are widely applied to various industries, and the harm to the health of human bodies is increasing. Thus, monitoring and analyzing the concentration of heavy metal ions in environmental samples is an urgent issue.
The traditional methods such as inductively coupled plasma mass spectrometry (ICP-MS), atomic Absorption Spectrometry (AAS) and inductively coupled plasma emission spectrometry (ICP-OES) have the advantages of being rapid and sensitive in heavy metal ion concentration detection, but the used instruments are high in price and large in size, and are not suitable for on-site analysis. The electrochemical method can be used for rapidly, economically and efficiently and sensitively carrying out in-situ analysis on heavy metal ions. Even heavy metal concentrations at ppb level can be measured by stripping voltammetry, so electrochemistry is the most preferred in situ measurement method.
However, electrochemical detection often uses noble metals as electrodes, such as gold electrodes, silver electrodes, etc., but cannot be popularized due to the high price of noble metals.
Disclosure of Invention
Based on this, it is necessary to provide a method for simultaneously detecting lead and arsenic, a detection electrode, an electrochemical sensor, and a preparation for the problem of using a noble metal as an electrode for electrochemical detection.
The first aspect of the invention provides a detection electrode comprising a graphite core and a nano-gold coating.
The graphite core surface has a graphite skin layer comprising a plurality of graphite layers.
The nano-gold coating is covered on the graphite surface layer and comprises a plurality of three-dimensional nano-gold particles.
Optionally, the graphite core is a pencil core with the surface layer removed of wax and clay.
The second aspect of the present invention provides a method for manufacturing a detection electrode, comprising the steps of:
a graphite core is provided, the surface of the graphite core having a graphite skin layer comprising a plurality of graphite layers.
And placing the graphite core in electrolyte, and preparing a nano-gold coating by electrodeposition, wherein the nano-gold coating is covered on the graphite surface layer and comprises a plurality of three-dimensional nano-gold particles.
Optionally, the electrolyte in the electrolyte solution comprises chloroauric acid and ammonium bromide, wherein the concentration of the chloroauric acid is 1mmol/L, and the concentration of the ammonium bromide is 10mmol/L.
Alternatively, the conditions of electrodeposition are: and depositing for 40-60 min under the constant voltage of-1.5V.
Optionally, the preparation method of the graphite core comprises the following steps:
polishing the pencil lead, cleaning the pencil lead by using an acetone and nitric acid solution, and applying voltage in a sulfuric acid solution to obtain the graphite core.
In a third aspect, the present invention provides an electrochemical sensor for simultaneously detecting lead and arsenic, the electrochemical sensor comprising a working electrode, a counter electrode and a reference electrode, the working electrode being the detection electrode described above or the detection electrode obtained by the above-described preparation method.
A fourth aspect of the invention provides a method for simultaneous detection of lead and arsenic, comprising the steps of:
the electrochemical sensor is placed in a solution to be measured, wherein the solution to be measured is an electrolyte solution, and the solution to be measured comprises lead ions and arsenic ions.
And (3) carrying out deposition for 500s under the condition of stirring and detecting voltage of-0.3 v, and detecting the elution peak current value of the electrochemical sensor by using a square wave elution voltammetry.
Optionally, the solution to be tested also comprises 0.5mol/L sulfuric acid solution.
Optionally, the pH value of the solution to be measured is 3.5-6.
The detection electrode comprises a graphite core and a nano-gold coating. The graphite surface layer comprises a plurality of graphite layers, so that the graphite surface layer has larger specific surface area, can provide larger accommodation space for the nano-gold coating, and can accommodate more nano-gold particles. The gold nanoparticle has a three-dimensional structure and a large specific surface area. Therefore, the whole specific surface area of the nano gold coating is larger, and the electrochemical activity of the detection electrode is high. In addition, the contact area between the gold nanoparticle with the three-dimensional structure and the graphite surface layer is increased, so that the gold nanoparticle coating layer is firmly combined with the graphite core, the stability of the detection electrode is better, the service life is long, and the data repeatability is good.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained according to the structures shown in these drawings without giving inventive effort to those skilled in the art.
FIG. 1A is an anodic stripping voltammogram of 100ppb As detected by NCG/GPL prepared at different deposition voltages; FIG. 1B is a plot of the current response of the prepared NCG/GPL to detect 100ppb As at different deposition voltages; FIG. 1C is an anodic stripping voltammogram of 100ppb As detected by NCG/GPL prepared at different deposition times; FIG. 1D is a plot of the current response of the NCG/GPL test 100ppb As prepared at different deposition times;
FIG. 2A is an anodic stripping voltammogram of 100ppb Pb detected by NCG/GPL prepared at different deposition voltages; FIG. 2B is a plot of the current response of the prepared NCG/GPL to detect 100ppb Pb at different deposition voltages; FIG. 2C is an anodic stripping voltammogram of 100ppb Pb detected by NCG/GPL prepared at different deposition times; FIG. 2D is a plot of the current response of the NCG/GPL to detect 100ppb Pb prepared at different deposition times;
FIG. 3A is a front SEM photograph of a graphite core of example 1; FIG. 3B is a side SEM photograph of a graphite core of example 1; FIG. 3C is a front SEM photograph of a second detection electrode of example 2; FIG. 3D is a side SEM photograph of a second sensing electrode of example 2;
FIG. 4A is an EDS diagram of a second detection electrode of example 2; FIG. 4B is an XRD pattern of the second detection electrode of example 2;
FIG. 5A is an anodic stripping voltammogram using NCG/Au electrodes, NG/GPL electrodes, and NCG/GPL electrodes to detect 100ppb Pb and 100ppbAs simultaneously; FIG. 5B is a bar graph of the corresponding stripping voltammetric peak current ratio;
FIG. 6A shows NCG/GPL electrode at 0.5. 0.5M H 2 SO 4 Anodic stripping voltammograms for simultaneous detection of arsenic and lead at different concentrations using SWASV under solution, fig. 6B is a corresponding calibration curve;
FIG. 7A is an anodic stripping voltammogram (inset is a calibration curve) of NCG/GPL electrodes using SWASV to detect lead at various concentrations in HAc-NaAc (pH=6) solution; FIG. 7B is an anodic stripping voltammogram (inset is a calibration curve) of NCG/GPL electrodes using SWASV to detect lead at different concentrations in HAc-NaAc (pH=3.5) solution;
fig. 8A is a plot of current response versus 100ppb simultaneous detection of lead and arsenic for the same NCG/GPL electrode multiple times, and fig. 8B is a plot of current response versus 100ppb simultaneous detection of lead and arsenic for different GPL/NCG electrodes prepared by the same experimental procedure.
The achievement of the object, functional features and advantages of the present invention will be further described with reference to the drawings in connection with the embodiments.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, are intended to fall within the scope of the present invention.
It should be noted that all directional indicators (such as upper and lower … …) in the embodiments of the present invention are merely used to explain the relative positional relationship, movement conditions, etc. between the components in a specific posture (as shown in the drawings), and if the specific posture is changed, the directional indicator is changed accordingly.
Furthermore, descriptions such as those referred to as "first," "second," and the like, are provided for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implying an order of magnitude of the indicated technical features in the present disclosure. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature.
Moreover, the technical solutions of the embodiments of the present invention may be combined with each other, but it is necessary to be based on the fact that those skilled in the art can implement the embodiments, and when the technical solutions are contradictory or cannot be implemented, it should be considered that the combination of the technical solutions does not exist, and is not within the scope of protection claimed by the present invention.
The embodiment of the application provides a detection electrode, which comprises a graphite core and a nano-gold coating. The graphite core surface has a graphite skin layer comprising a plurality of graphite layers. The nano-gold coating is covered on the graphite surface layer and comprises a plurality of three-dimensional nano-gold particles.
The surface of the graphite core is provided with a graphite surface layer, and graphite is layered into small-volume graphite sheets or graphite particles. Referring to fig. 1, there is a gap between two adjacent graphite layers, or between one graphite layer and several other graphite layers.
The formation modes of the gap at least comprise two modes: illustratively, the material of the surface of the graphite core is graphite, and fine grooves or holes are formed in the surface of the graphite core by machining. The walls of the grooves or holes are graphite layering, and the spaces of the grooves or holes are gaps among the graphite layering.
Also illustratively, the materials such as the surface of the graphite core are graphite and readily erodable materials (such as waxes and clay) which are removed by solution erosion to form fine grooves or holes in the surface of the graphite core. The walls of the grooves or holes are graphite layering, and the spaces of the grooves or holes are gaps among the graphite layering.
Because of the existence of a plurality of graphite layering, the surface of the graphite core is rugged, and compared with a structure with a flat surface, the graphite core has larger specific surface area. Therefore, the graphite surface layer can provide a larger accommodating space for the nano-gold coating, namely, more nano-gold particles can be accommodated.
The nano-gold coating comprises a plurality of three-dimensional nano-gold particles. The three-dimensional nano-gold particles comprise small protrusions extending in multiple directions in a three-dimensional space. The three-dimensional nano gold particles are connected together, so that the whole nano gold coating is of a three-dimensional network structure with multiple nano branches and multiple nano holes, and can be called Nano Coral Gold (NCG).
In the related art, some of the nano-gold coatings are nano-gold films or nano-dendrites. The nano gold film is of a planar structure and basically does not comprise a nano branch structure. The nanobranches, although also comprising a plurality of nanobranches, extend substantially in the same plane. I.e. the nano-dendrite structure is also substantially planar. The nano coral gold is a three-dimensional network structure, so that the specific surface area of the nano coral gold is obviously larger than that of the nano branch structure.
The graphite surface layer can contain more nano gold particles. Therefore, the whole specific surface area of the nano gold coating is larger, more active sites are provided, more metal ions to be detected can be combined, and therefore, the electrochemical activity of the detection electrode is high.
In addition, the contact area between the nano coral gold and the graphite surface layer is increased, the nano gold coating layer is firmly combined with the graphite core, the stability of the detection electrode is good, the service life is long, and the data repeatability is good.
The detection electrode comprises a graphite core and a nano-gold coating. The graphite surface layer comprises a plurality of graphite layers, so that the graphite surface layer has larger specific surface area, can provide larger accommodation space for the nano-gold coating, and can accommodate more nano-gold particles. The gold nanoparticle has a three-dimensional structure and a large specific surface area. Therefore, the whole specific surface area of the nano gold coating is larger, and the electrochemical activity of the detection electrode is high. In addition, the contact area between the gold nanoparticle with the three-dimensional structure and the graphite surface layer is increased, so that the gold nanoparticle coating layer is firmly combined with the graphite core, the stability of the detection electrode is better, the service life is long, and the data repeatability is good.
Optionally, the graphite core is a pencil lead (GPL) with the surface layer removed of wax and clay. The pencil lead is made up by mixing graphite, clay and wax according to a certain proportion. And removing wax and clay on the surface layer of the pencil lead through the reagent to form a large number of graphite layering. The graphite of the graphite core is uniformly distributed in a layering manner, and the manufacturing cost is low.
The second aspect of the present invention provides a method for manufacturing a detection electrode, comprising the steps of:
a graphite core is provided, the surface of the graphite core having a graphite skin layer comprising a plurality of graphite layers.
And placing the graphite core in electrolyte, and preparing a nano-gold coating by electrodeposition, wherein the nano-gold coating is covered on the graphite surface layer and comprises a plurality of three-dimensional nano-gold particles.
The preparation method has the technical characteristics corresponding to the detection electrode, so that the preparation method has the corresponding technical effects and is not repeated here.
Optionally, the electrolyte in the electrolyte solution comprises chloroauric acid and ammonium bromide, wherein the concentration of the chloroauric acid is 1mmol/L, and the concentration of the ammonium bromide is 10mmol/L.
The reaction formula is as follows:
AuCl 4 - +3e-+4H + ＝Au+4HCl
by HAuCl 4 And NH 4 Br electrodepositing NCG on gold electrode, HAuCl 4 Reduced to Jin He, and the gold core adsorbs Br-. NH due to electrostatic attraction 4 + Can be combined with Br - The surface position of the gold core is occupied, so that the mutual collision between the nanospheres can be effectively inhibited to form nano particles, NH 4 + The hydrogen atom connected with the nitrogen atom is smaller, and the gold core cannot be completely wrapped. Au atoms can smoothly pass through NH 4 The Br molecular gaps are bound to nanospheres, so that the unwrapped gold core can continue to grow and form NCG on the electrode.
Alternatively, the conditions of electrodeposition are: and depositing for 40-60 min under the constant voltage of-1.5V.
When nano coral gold is deposited, the deposition voltage and the deposition time are two important parameters. The NCG prepared under different conditions has different detection sensitivity to heavy metals. With the increase of the deposition time of the nano gold on the GPL, the NCG structure is gradually constructed, the nano gold coating becomes thicker, and the specific surface area is gradually increased. However, too long deposition time can also cause a part of nano gold particles to separate from GPL, so that the effect of heavy metal ion detection is weakened. And when the deposition time is too long, the nano gold particles of the nano gold coating are more and more dense, and the specific surface area of the nano gold coating can be reduced after reaching a certain degree. The detection electrode prepared under the conditions has higher detection sensitivity in electrochemical detection of arsenic and lead.
As shown in FIG. 1, the prepared detection electrode (NCG/GPL electrode) is most favorable for electrochemical detection of arsenic when the deposition voltage is-1.5V and the deposition time is 45 min.
And lead ions were detected electrochemically against NCG/GPL electrodes. As shown in FIG. 2, the prepared NCG/GPL electrode is most favorable for electrochemical detection of lead when the deposition voltage is-1.5V and the deposition time is 60min. However, the increase of the detection signal for lead ions is not large when compared with the deposition time of 45 min. Thus, preferably, in combination, for uniform electrode preparation, a deposition time of 45min at-1.5V was chosen as the conditions for NCG/GPL preparation.
Optionally, the preparation method of the graphite core comprises the following steps:
polishing the pencil lead, cleaning the pencil lead by using an acetone and nitric acid solution, and applying voltage in a sulfuric acid solution to obtain the graphite core.
Since the pencil lead surface contains a large amount of wax and clay, it is necessary to remove the wax and clay on the surface by surface polishing the GPL with sandpaper. The GPL was then sonicated in acetone and nitric acid solutions, respectively, to clean the residual wax and clay. And then GPL is at H 2 SO 4 And applying voltage in the solution, and performing electrochemical dissolution on wax positioned between graphite particles to maximally improve the conductivity of the GPL platform, wherein the applied voltage is-1.5V. After the steps, the wax and clay on the surface of the pencil lead are removed, and the space originally occupied by the wax and the clay forms fine grooves or holes. The walls of the grooves or holes are graphite layering, and the spaces of the grooves or holes are gaps among the graphite layering.
In some embodiments, the sonication time in the graphite core preparation step is 15 minutes.
In some embodiments, H in the graphite core preparation step 2 SO 4 The concentration was 0.5mol/L.
In some embodiments, the voltage in the graphite core preparation step is-1.5V and the processing time is 300s.
The embodiment of the application also provides an electrochemical sensor for simultaneously detecting lead and arsenic, wherein the electrochemical sensor comprises a working electrode, a counter electrode and a reference electrode, and the working electrode is the detection electrode or the detection electrode obtained by the preparation method.
A fourth aspect of the invention provides a method for simultaneous detection of lead and arsenic, comprising the steps of:
the electrochemical sensor is placed in a solution to be measured, wherein the solution to be measured is an electrolyte solution, and the solution to be measured comprises lead ions and arsenic ions.
And (3) carrying out deposition for 500s under the condition of stirring and detecting voltage of-0.3 v, and detecting the elution peak current value of the electrochemical sensor by using a square wave elution voltammetry.
Optionally, the solution to be tested also comprises 0.5mol/L sulfuric acid solution.
Optionally, the pH value of the solution to be measured is 3.5-6.
Example 1
Preparation of graphite core
Since the surface of the pencil lead contains a large amount of wax and clay, it is necessary to surface polish the pencil lead by using sandpaper, and then sonicate the pencil lead in acetone and nitric acid solutions for 15 minutes, respectively. Activating the pencil lead, namely H at 0.5mol/L 2 SO 4 And (3) applying voltage of-1.5V to the solution for 300s, and finally drying and preserving to obtain the graphite core GPL.
Example 2
Immersing the GPL of example 1 in a HAuCl-containing solution 4 And NH 4 In solution of Br (i.e., electrolyte), HAuCl 4 Is 1mmol/L, NH 4 The concentration of Br was 10mmol/L.
Then, electrodepositing is carried out under constant voltage, and NCG is constructed on the surface of the GPL, so that a detection electrode (NCG/GPL) is obtained. The prepared detection electrode is washed by ultrapure water and naturally dried at room temperature.
Electrochemical testing was performed using a three electrode system: NCG/GPL is a working electrode, a calomel electrode is a reference electrode, and a platinum electrode is a counter electrode. To 0.5. 0.5M H containing 100ppb Pb (II) and 100ppb As (III), respectively 2 SO 4 The electrolyte solution is a test solution, a voltage of-0.3V is applied to a working electrode for 500s through an electrochemical workstation, divalent lead and trivalent arsenic pre-enriched on the surface of the working electrode are reduced to zero valence, and then a Square Wave Anodic Stripping Voltammetry (SWASV) is used for scanning within the potential range of-0.3V to +0.3V, so that the zero valence on the surface of the electrodeLead and zero-valent arsenic are rapidly oxidized into divalent lead and trivalent arsenic, a stripping voltammetric peak appears at-0.05V for Pb (II), a stripping voltammetry An Feng appears at +0.15V for As (III), the current value of the stripping peak gradually increases along with the increase of the ion concentration, and a working curve is drawn according to the peak current intensity and the ion concentration. When the working electrode is inserted into the test solution, the process of enriching the divalent lead and trivalent arsenic in the test solution to the surface of the working electrode is pre-enrichment.
Since nano coral gold is deposited, deposition voltage and deposition time are two important parameters. The NCG prepared under different conditions has different detection sensitivity to heavy metals. With the increase of the deposition time of the nano gold on the GPL, the structure of the NCG is gradually constructed, the coating is thickened, and the specific surface area is gradually increased. However, the nano gold is separated from the GPL due to the excessively long deposition time, so that the effect of heavy metal ion detection is weakened.
Under the condition that the deposition time is 45min, the detection electrodes are respectively prepared under the conditions that the deposition voltage is-1V, -1.3V, -1.5V, -1.7V and-2.0V, and the standard solution of 100ppb As is respectively detected by the corresponding detection electrodes by adopting the method. The detection results are shown in fig. 1A and 1B.
And under the condition of the deposition voltage of-1.5V, respectively preparing detection electrodes under the conditions of the deposition time of 5min, 20min, 45min and 60min, and respectively detecting the standard solution of 100ppb As by adopting the method by using the corresponding detection electrodes. The detection results are shown in fig. 1C and 1D.
Referring to fig. 1A, 1B, 1C and 1D, when the deposition voltage is-1.5V and the deposition time is 45min, the prepared NCG/GPL electrode (hereinafter referred to as a first detection electrode for convenience of description) is most advantageous for electrochemical detection of arsenic.
And under the condition that the deposition time is 45min, respectively preparing detection electrodes under the conditions that the deposition voltage is-1V, -1.3V, -1.5V, -1.7V and-2.0V, and respectively detecting 100ppb Pb standard solution by adopting the method by using the corresponding detection electrodes. The detection results are shown in fig. 2A and 2B.
And under the condition of the deposition voltage of-1.5V, respectively preparing detection electrodes under the conditions of the deposition time of 5min, 20min, 45min and 60min, and respectively detecting 100ppb Pb standard solution by adopting the method by using the corresponding detection electrodes. The detection results are shown in fig. 2C and 2D.
Referring to fig. 2A, 2B, 2C and 2D, the prepared NCG/GPL electrode (hereinafter referred to as a second detection electrode for convenience of explanation) is most advantageous for electrochemical detection of lead when the deposition voltage is-1.5V and the deposition time is 60min. However, the increase of the detection signal of the lead ions is not large compared with the first detection electrode. Considering that the second detection electrode is used for electrochemically detecting arsenic compared with the first detection electrode, the detection signal of arsenic ions is obviously reduced, and therefore, under comprehensive consideration, the conditions of-1.5V and 45min can be selected as conditions for preparing NCG/GPL. Namely, the second detection electrode is used as a detection electrode for simultaneously detecting lead and arsenic.
Data characterization
The graphite core and the second detection electrode of example 1 were each characterized by Scanning Electron Microscopy (SEM). Fig. 3A, 3B show SEM images of the front and side faces of the graphite core surface. On the graphite core, the surface graphite is layered more, so that the specific surface of the graphite core is obviously larger, and more nano coral gold can be modified to increase electrochemical activity. Fig. 3C, 3D show SEM images of the front and side faces of NCG on the surface of the graphite core. The NCG exhibits a coral-like structure when viewed from the front, covering almost the entire electrode surface, while nano corals grow in different directions. The NCG exhibits a huge network structure as seen from the side, while the intermediate pores are apparent. The pores enable heavy metal ions to easily enter the gold surface for electrochemical reaction, and the large surface area of NCG is favorable for electrochemical detection, so that higher detection sensitivity is finally realized.
The second detection electrode was characterized using XRD and EDS. The characteristic peak of Au element can be clearly seen from EDS analysis results (fig. 4A) of the second detection electrode. The crystal phase information of the second detection electrode was analyzed by XRD. As shown in fig. 4B, the well-defined (002) peak at 26.34 ° represents GPL graphite. In NCG/GPL, the intensity of the graphite peak is reduced, and at the same time, a distinct characteristic diffraction peak at 38.09 degrees can be clearly seen in the inset, corresponding to the (111) crystal plane of the nanogold.
To further verify the feasibility of detection of Pb (II) and As (III) by NCG/GPL electrode pairs, I designed a control experiment.
Comparative example 1
NCG is prepared on the gold electrode by adopting a preparation method of the gold electrode and the second detection electrode, so that NCG/Au is formed.
Comparative example 2
Impregnation of HAuCl with graphite core of example 1 4 In the solution, electrodepositing is carried out for 45min under the condition of constant voltage of-1.5 v, and nano gold (NG/GPL) is prepared on a graphite core. The whole nano gold prepared by the method is a nano gold film.
The standard solutions in which 100ppb Pb (II) and 100ppb As (III) were simultaneously present were detected using the NCG/Au electrode of comparative example 1, the NG/GPL electrode of comparative example 2, and the second detection electrode NCG/GPL, respectively.
Referring to FIG. 5, both the NCG/Au electrode (curve a) and the NG/GPL electrode (curve b) had dissolution volts An Feng current for Pb (II) and As (III), but the dissolution volt-ampere peak current for the NCG/GPL electrode (curve c) at-0.05V and +0.15V increased significantly due to the excellent conductivity of the NCG/GPL electrode. To sum up. The NCG/GPL electrode prepared by the invention can be used for enriching Pb (II) and As (III) and performing sensitive electrochemical detection.
Example 3
The second detection electrode measures Pb (II) and As (III)
Pb (II) and As (III) were detected at different concentrations under the conditions of an optimal deposition voltage of-0.3V and a deposition time of 500 s.
Pb (II) and As (III) were detected at different concentrations. Electrochemical testing was performed using a three electrode system: the second detection electrode is a working electrode, the calomel electrode is a reference electrode, and the platinum electrode is a counter electrode. In a concentration of 0.5. 0.5M H containing Pb (II) and As (III) 2 SO 4 The electrolyte solution is a test solution, and a voltage of-0.3V is applied to the working electrode for 500s by an electrochemical workstation, and the divalent lead and trivalent arsenic pre-enriched on the surface of the working electrode are reduced intoThe zero-valent lead and the zero-valent arsenic on the surface of the electrode are rapidly oxidized into divalent lead and trivalent arsenic by scanning in the potential range of-0.3V to +0.3V by using a Square Wave Anodic Stripping Voltammetry (SWASV), the stripping voltage An Feng appears at-0.05V for Pb (II), the stripping voltage An Feng appears at +0.15V for As (III), the stripping peak current value is gradually increased along with the increase of the ion concentration (figure 6A), a working curve is drawn according to the peak current intensity and the ion concentration (figure 6B), the peak current intensity and the ion concentration have good linear relation in the range of 10-100ppb, and the linear correlation coefficient R2 is 0.993 (As) and 0.964 (Pb) respectively. The detection limits for arsenic and lead were 0.1ppb, 0.06ppb (S/n=3), respectively, and the LOD reached was well below the drinking water limit.
Example 4
On the basis of example 3, see fig. 7, lead solutions of different concentrations were detected in 0.1M HAc-NaAc buffer at ph=6 (a) and ph=3.5 (B), respectively, using a second detection electrode. The linear fitting (inset) was performed at a concentration range of 2.5-100ppb, with R2 values of 0.938 (ph=6) and 0.994 (ph=3.5), respectively, all having good linear relationships. The second detection electrode has little difference in detection signals of lead at different pH values, and the quantitative analysis capability of the electrode in a wider pH range is proved.
Example 5
Stability and reproducibility are important indicators for evaluating the performance of the detection method. The repeatability of the NCG/GPL electrodes was determined by repeating the test multiple times in the same test solution (100 ppb arsenic and 100ppb lead solution) using the same NCG/GPL electrode. The test conditions were the same as in example 3. Referring to fig. 8a, rsd was 4.13% (arsenic) and 2.79% (lead), respectively. As shown in fig. 8B, a plurality of NCG/GPL electrodes were prepared by the preparation method of example 2, and the reproducibility of the NCG/GPL electrodes was determined by performing a test on the same test solution (100 ppb arsenic and 100ppb lead solution) with the plurality of NCG/GPL electrodes. The test conditions were the same as in example 3.RSD values were 2.58% (arsenic) and 3.49% (lead), respectively. These results indicate that GPL/NCG has good stability and reproducibility.
To further examine the applicability of the method of the present invention, pb (II) and As (III) in various sources of water samples including industrial wastewater from mining and smelting sites were tested by the method of example 3, the above solutions were examined and analyzed by a sensor comprising a second detection electrode, all samples were measured in parallel three times, and the results are shown in table 1. Wherein the standard concentration is the result of detection by ICP-MS.
TABLE 1
As can be seen from Table 1, the recovery rate of the above detection was between 90% and 109%, and the relative standard deviation was between 5% and 10%, indicating that the constructed sensor was feasible for simultaneous detection analysis of Pb (II) and As (III) actual samples.
In summary, the electrochemical sensor of the invention can be used for measuring Pb (II) and As (III) concentrations and Pb (II) and As (III) contents in industrial wastewater; the preparation method of the electrochemical sensor has simple preparation process and simple operation.
In the above technical solution of the present invention, the above is only a preferred embodiment of the present invention, and therefore, the patent scope of the present invention is not limited thereto, and all the equivalent structural changes made by the content of the present specification and the accompanying drawings or the direct/indirect application in other related technical fields are included in the patent protection scope of the present invention under the technical concept of the present invention.
Claims (7)
1. The preparation method of the detection electrode is characterized by comprising the following steps of:
providing a graphite core, wherein the surface of the graphite core is provided with a graphite surface layer, and the graphite surface layer comprises a plurality of graphite layering layers;
placing the graphite core in electrolyte, and preparing a nano-gold coating by electrodeposition, wherein the nano-gold coating is covered on the graphite surface layer and comprises a plurality of three-dimensional nano-gold particles;
the graphite core is a pencil core from which the surface layer of wax and clay are removed; the preparation method of the graphite core comprises the following steps:
polishing the pencil lead, cleaning the pencil lead by using an acetone and nitric acid solution, and applying voltage in a sulfuric acid solution to obtain the graphite core.
2. The method for manufacturing a detection electrode according to claim 1, wherein the electrolyte in the electrolyte solution comprises chloroauric acid and ammonium bromide, the concentration of the chloroauric acid is 1mmol/L, and the concentration of the ammonium bromide is 10mmol/L.
3. The method for manufacturing a detection electrode according to claim 2, wherein the electrodeposition conditions are: and depositing for 40-60 min under the constant voltage of-1.5V.
4. An electrochemical sensor for simultaneous detection of lead and arsenic, characterized in that it comprises a working electrode, a counter electrode and a reference electrode, the working electrode being the detection electrode obtained by the method of any one of claims 1 to 3.
5. A method for simultaneous detection of lead and arsenic, comprising the steps of:
placing the electrochemical sensor of claim 4 in a solution to be measured, wherein the solution to be measured is an electrolyte solution, and the solution to be measured comprises lead ions and arsenic ions;
and (3) carrying out deposition for 500s under the condition of stirring and detecting voltage of-0.3 v, and detecting the elution peak current value of the electrochemical sensor by using a square wave elution voltammetry method.
6. The method for simultaneous detection of lead and arsenic according to claim 5, wherein the solution to be measured further comprises a sulfuric acid solution of 0.5mol/L.
7. The method for simultaneous detection of lead and arsenic according to claim 5, wherein the pH value of the solution to be detected is 3.5 to 6.
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| Nano-Coral Gold (NCG) Electrode for Electrochemical Determination of Arsenic (III) in Industrial Wastewater by Square Wave Anodic Stripping Voltammetry (SWASV);Lan Yang等;Analytical Letters;第55卷(第16期);2639-2649 * |
| Simultaneous electrochemical determination of arsenic, copper, lead and mercury in unpolluted fresh waters using a vibrating gold microwire electrode;Georgina M.S. Alves等;Analytica Chimica Acta;20110723;第703卷;1-7 * |
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